1. Field of the Invention
The present invention relates to a reflective type liquid crystal display device.
2. Description of the Related Art
There are transmitting-type liquid-crystal display devices in which light passes through the liquid crystal panel from the rear to the front thereof, and reflective-type liquid-crystal display devices in which a light enters from the front of the liquid crystal panel, is reflected at a reflecting layer at the rear of the liquid-crystal panel and exits from the front side of the liquid crystal panel. The transmitting type liquid crystal display device can include a back-light or the like on the rear of the liquid crystal panel to enhance brightness and contrast. However, the reflective type liquid crystal display device cannot use a back light, and thus brightness and contrast are relatively low. Recently, a demand for a reflective-type liquid crystal display device with increased brightness and contrast, and color, has arisen.
A reflective-type liquid crystal display device providing with color is disclosed, for example, in the report of the Japanese electronic display society, "ED85-40, p81". This is shown in FIGS. 6 and 7 in the attached drawings. In FIGS. 6 and 7, the layer of liquid crystal 3 is arranged between the first and second plates 1 and 2, the first plate 1 is transparent, and the second plate 2 has a reflecting surface 4 for reflecting a light entering from the first plate 1. The layer of liquid crystal 3 comprises a guest-host phase change type liquid crystal having a dichroic dye 5 mixed therein. The first plate 1 has a color filter 6 formed on the inner surface thereof.
In the phase-change liquid crystal display device, molecules of the liquid crystal are in a twisted cholesteric phase when the voltage is not applied, as shown in FIG. 6, and into a nematic phase, in which molecules of the liquid crystal are aligned perpendicular to the plates 1 and 2, when the voltage is applied, as shown in FIG. 7. Therefore, in the condition of FIG. 6, the particles of the dichroic dye 5 with the molecules of the liquid crystal 3 are generally randomly distributed, and the light inputting from the first plate 1 impinges against the particles of the dichroic dye 5 and absorbed therein to produce a black display. In the condition of FIG. 7, the particles of the dichroic dye 5 with the molecules of the liquid crystal 3 become perpendicular to the plates 1 and 2, and the light entering from the first plate 1 passes through the particles of the dichroic dye 5. Thus, the light entering from the first plate 1 is reflected at the reflecting layer 4 of the second plate 2, and passes through the color filter 6 to produce a color display corresponding to the color or colors of the color filter 6. When the pixel electrode corresponding to all colors in one pixel are switched on, a white display is produced.
In the above described prior art reflective-type liquid crystal display device, to produce a color display or a white display, the light entering from the first plate 1 must initially pass through the color filter 6, then through the layer of liquid crystal 3 and the dichroic dye 5, and be reflected at the reflecting layer 4 to return to the layer of liquid crystal 3, the dichroic dye 5, and the color filter 6. However, the transmissivity of the color filter 6 is low, and the amount of the light first passing through the color filter 6 is reduced. Also, since the light passing through the color filter 6 further passes through the layer of liquid crystal 3 and the dichroic dye 5, and returns to the color filter 6 after reflected at the reflecting layer 4, brightness of the color display and the white display thus obtained is relatively low.